Apparatus and method for producing silicon semiconductor single crystal

ABSTRACT

The present invention provides an apparatus and a method for producing a silicon semiconductor single crystal which can stabilize and homogenize an amount of precipitated oxygen in the direction of the crystal growth axis when growing a silicon semiconductor single crystal. The apparatus for producing a silicon semiconductor single crystal by the Czochralski method comprises a main growth furnace having a crucible retaining silicon melt disposed therein for growing a silicon semiconductor single crystal, and an upper growth furnace for housing therein and cooling the silicon semiconductor single crystal pulled from the silicon melt, wherein the upper growth furnace communicated to a ceiling section of the main growth furnace is provided with an upper insulating member for surrounding a pulled silicon semiconductor single crystal.

TECHNICAL FIELD

The present invention relates to an apparatus for producing a siliconsemiconductor single crystal using the Czochralski method (referred toas a CZ method hereinafter), and a method for producing a siliconsemiconductor single crystal with the apparatus.

BACKGROUND ART

Conventionally, in the growth of a silicon semiconductor single crystalusing the CZ method, polysilicon is charged in a crucible provided in agrowth furnace of an apparatus for producing a silicon semiconductorsingle crystal, the polysilicon is melted to silicon melt by heating thepolysilicon with a heater provided around the crucible, and after a seedcrystal is dipped into the melt, the seed crystal is pulled above thesilicon melt while rotating it gently to grow a silicon semiconductorsingle crystal having a substantially cylindrical constant diameterportion. Then the pulled silicon semiconductor single crystal is cut andground to leave the constant diameter portion, and becomes a siliconsemiconductor wafer through a wafer shaping process. The thus obtainedsilicon semiconductor wafer is used as a semiconductor device substratefor fabricating an integrated circuit or the like on the surface layerof which is formed an electric circuit.

In the process of forming an electric circuit on the surface layer ofthe silicon semiconductor wafer, oxygen atoms contained in the siliconsemiconductor wafer bond to silicon atoms to form oxide precipitatessuch as BMD (Bulk Micro Defect) inside the silicon semiconductor wafer.It is known that the oxide precipitates such as BMD capture (or getter)excess contamination atoms such as heavy metal atoms contaminated in thesemiconductor device fabricating process to improve properties andyields of semiconductor devices. Therefore, by using a siliconsemiconductor wafer substrate containing larger amounts of oxideprecipitates such as BMD, it is possible to improve yields ofsemiconductor devices formed on a surface layer of the substrate.

The amount of oxide precipitates depends on a concentration of oxygenoriginally contained in the silicon semiconductor wafer as well as onthermal history of the silicon semiconductor wafer for a period fromduring the crystal growth up to just prior to the semiconductor devicefabricating process. However, generally there is a standard for aconcentration of oxygen contained in a silicon semiconductor wafer,which cannot be changed readily.

Also it is known that in the silicon semiconductor single crystal, evenif distribution of an oxygen concentration in the direction of thegrowth axis is homogeneous, distribution of the amount of precipitatedoxygen exists in a state where it is relatively large in the seed sideof the grown crystal and is relatively small in the melt side. It isconsidered that this phenomenon is due to the distribution in the axialdirection of thermal history in a relatively low temperature zone wherenuclei of the oxide precipitates are formed and grow in the singlecrystal.

Then there is disclosed a technique for adjusting the thermal history toa desired value during a processing period from growing a siliconsemiconductor single crystal up to manufacturing a silicon semiconductorwafer therefrom. For instance, JPA 83-120591 discloses a method ofincreasing oxygen precipitation by heating a silicon semiconductorsingle crystal during its growth to adjust the thermal history, and inJPA 90-263792, the method of annealing a silicon semiconductor singlecrystal after its growth and the like are examined.

In the method of heating a silicon semiconductor single crystal duringits growth, however, there are required large scale reconstruction forinstalling a heating apparatus of heating a grown silicon semiconductorsingle crystal in a producing apparatus and a power for heating thegrown crystal; the method cannot be regarded as an efficient method fromthe viewpoint of cost and operability. Further, a temperature balanceduring growth of a silicon semiconductor single crystal is forciblychanged, so that dislocations are created in the grown crystal, therebythe commercialization thereof being disadvantageously impossible.

On the other hand, in the method of annealing a silicon semiconductorsingle crystal after its growth, it is conceivable to anneal the siliconsemiconductor single crystal in the ingot state or in the wafer state,but an expensive apparatus is required in either case, and in addition,running cost for the apparatus for annealing as described above isgenerally high, and therefore this method is inefficient in view of theproduction cost. Further, this method in which oxygen precipitation in acrystal is controlled by means of annealing has such troubles ascontamination by heavy metals during the annealing process; so suchproblems persist in this method.

DISCLOSURE OF THE INVENTION

With the foregoing drawbacks of the prior art in view, it is an objectof the present invention to provide an apparatus and a method forproducing a silicon semiconductor single crystal which can stabilize andhomogenize an amount of precipitated oxygen in the direction of thecrystal growth axis when growing a silicon semiconductor single crystal.

To achieve the above described object, an apparatus for producing asilicon semiconductor single crystal according to the present inventionresides in an apparatus for producing a silicon semiconductor singlecrystal by the Czochralski method which comprises a main growth furnacehaving a crucible retaining silicon melt disposed therein for growing asilicon semiconductor single crystal, and an upper growth furnace forhousing therein and cooling the silicon semiconductor single crystalpulled from the silicon melt, wherein the upper growth furnacecommunicated to a ceiling section of the main growth furnace is providedwith an upper insulating member for surrounding a pulled siliconsemiconductor single crystal.

To make oxygen precipitated more in a silicon semiconductor singlecrystal, it is necessary to form therein nuclei for causing oxygenprecipitation during crystal growth and to make the nuclei grown tolarge sizes. When a silicon semiconductor single crystal is subjected toheat treatment at a constant temperature, nuclei of oxide precipitateslarger than the critical radius at the temperature grow to larger sizes,while those smaller than the critical radius are annihilated from insideof the silicon semiconductor single crystal. The critical radius of thenuclei of oxide precipitates becomes larger as the heat treatmenttemperature becomes higher. Therefore, to form BMD capable of getteringcontaminants in a silicon semiconductor wafer, it is important to makethe nuclei of oxide precipitates to sizes where the nuclei are notannihilated with heat treatment in the semiconductor device fabricatingprocess. For that purpose, it is necessary to make the nuclei of oxideprecipitates larger by adding heat treatment or thermal history more ata lower temperature than the heat treatment temperature in thesemiconductor device fabricating process.

After a silicon semiconductor single crystal is formed in a growthfurnace in a silicon semiconductor single crystal producing apparatus,the silicon semiconductor single crystal is pulled into the upper growthfurnace and is allowed to cool down therein; therefore by adjusting thecooling rate at the low temperature section to a desired value, thesilicon semiconductor single crystal is able to receive thermal historymore to promote the formation of BMD.

To easily grow the silicon semiconductor single crystal having suchquality as described above, the simple and best method is to arrange anupper insulating member for keeping warm a crystal pulled into the uppergrowth furnace such that the silicon semiconductor single crystalreceives sufficiently thermal history at the low temperature sectionwhen the silicon semiconductor single crystal cools down. The upperinsulating member may have a length almost similar to the full length ofthe upper growth furnace or may be arranged so as to keep warm at leastabout one twentieth of the full length of the upper growth furnace. Whena length of the upper insulating member arranged in the upper growthfurnace is less than one twentieth of the full length of the uppergrowth furnace, it is difficult to realize the sufficient keeping warmeffect.

To sufficiently and suitably achieve the keeping warm effect for asilicon semiconductor single crystal at a low temperature area, atemperature inside the upper growth furnace communicated to the ceilingsection of the growth furnace provided in the apparatus for producing asilicon semiconductor single crystal is 800° C. or less, or the uppergrowth furnace is arranged such that, even when a length of the upperinsulating member is minimal, a temperature section of from 400° C. to650° C. is kept warm; by adjusting the upper insulating member in such away that thermal history of the silicon semiconductor single crystal inthe above described temperature area become longer, it is possible tomake the amount of precipitated oxygen larger and also to ensure stableoxygen precipitation along the full length of a crystal.

Especially, with an apparatus for producing a silicon semiconductorsingle crystal having the construction of the inventive apparatus, whengrowing a silicon semiconductor single crystal, as a first half portionof the crystal corresponding to the seed crystal side passes through theinsulating member arranged in the upper growth furnace during growth ofa second half portion of the crystal, it can receive sufficientlythermal history in the low temperature section; although the second halfportion of the silicon semiconductor single crystal does not passthrough the insulating member during growth of the single crystal, whenthe silicon semiconductor single crystal is pulled into the upper growthfurnace and cooled down to such a low temperature as the siliconsemiconductor single crystal can be taken out, the second half portionis surrounded by the insulating member of the upper growth furnace, sothat the second half portion can receive sufficiently thermal history inthe low temperature section like the first halt portion of the siliconsemiconductor single crystal even after the crystal is separated fromthe silicon melt.

By taking the above described countermeasures, although there isgenerated a slight difference between the first half potion and thesecond half portion of the crystal in terms of the time when the siliconsemiconductor single crystal is kept warm at a low temperature due tooperating conditions for growing the silicon semiconductor singlecrystal or other reasons, the difference in an amount of precipitatedoxygen between the first half portion and the second half portion of thecrystal is substantially smaller as compared to that when the insulatingmember is not used; it is possible to obtain a crystal with the amountof precipitated oxygen homogenized along the full length of the crystalstraight body.

Further, an amount of precipitated oxygen generated in a siliconsemiconductor single crystal depends largely on the duration of thermalhistory in the low temperature section when the crystal is cooled down;by adjusting a length of the upper insulating member arranged in theupper growth furnace of the producing apparatus to a kind or a qualityof a silicon semiconductor single crystal to be grown, it is possible tomore efficiently grow a silicon semiconductor single crystal having adesired amount of precipitated oxygen. An upper insulating member in theupper growth furnace may be exchanged with one having a differentlength, whenever growing a silicon semiconductor single crystal,according to a crystal kind such as a diameter and a length of thesilicon semiconductor single crystal to be pulled or an oxygenconcentration in the crystal. Also it is preferable to provide aplurality of upper insulating members themselves piled up in thedirection of the crystal growth axis in the upper growth furnace, sothat the number of the upper insulating members can be changed forchanging a temperature range of a lower temperature section of thecrystal to be kept warm according to a desired amount of precipitatedoxygen in the silicon semiconductor single crystal.

With the above described producing apparatus, it is possible to adjustsuitably a temperature range width of a low temperature section of acrystal to be kept warm by changing a length of the upper insulatingmember arranged in the upper growth furnace; it is possible to controlan amount of precipitated oxygen in the silicon semiconductor singlecrystal to be pulled to a desired value.

On the other hand, the upper insulating member arranged in the uppergrowth furnace for keeping warm the silicon semiconductor single crystalis exposed to a high temperature ranging from several hundreds c toabout 800° C. even in the upper growth furnace; it is preferable to usean upper insulating member made of the materials shaped from the samecarbon fiber as the insulating member for a heater or the like providedin the growth furnace for growing a silicon semiconductor singlecrystal. Further, in order to prevent impurities or the like out of theinsulating member from flying into the growth furnace, it is desirableto cover a surface of the upper insulating member with high puritygraphite materials or high purity graphite materials with a surfacecoated with a film of pyrolytic carbon or silicon carbide, or withmetallic materials containing a metal selected from the group consistingof iron, nickel, chromium, copper, titanium, tungsten, and molybdenum asthe main ingredient.

With the apparatus described above, as an amount of precipitated oxygenin a silicon semiconductor single crystal in the direction of thecrystal growth axis can be stabilized almost uniformly, there is reducedvariations in an amount of precipitated oxygen between individualproducts generated when silicon semiconductor wafers obtained fromrespective portions of a crystal are subjected to heat treatment of somekind such as device simulation in the next process; therefore it ispossible to stabilize device quantity and production yield.

A first aspect of the method for producing a silicon semiconductorsingle crystal according to the present invention is to produce thesilicon semiconductor single crystal by the use of the apparatus forproducing a silicon semiconductor single crystal according to thepresent invention.

A second aspect of the method for producing a silicon semiconductorsingle crystal according to the present invention resides in a methodfor producing a silicon semiconductor single crystal by the Czochralskimethod, wherein the silicon semiconductor single crystal pulled from acrucible is grown keeping warm a portion thereof with a temperature of800° C. or less without heating it from the outside.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional explanatory view showing anembodiment of an apparatus for producing a silicon semiconductor singlecrystal according to the present invention;

FIG. 2 shows another embodiment of an apparatus for producing a siliconsemiconductor single crystal according to the present invention, whereina part (a) is a schematic cross-sectional explanatory view of anessential part thereof, and a part (b) is a perspective picked out viewof an upper insulating member;

FIG. 3 shows a further embodiment of an apparatus for producing asilicon semiconductor single crystal according to the present invention,wherein a part (a) is a schematic cross-sectional explanatory view of anessential part thereof, and a part (b) is a perspective picked out viewof an upper insulating member;

FIG. 4 shows a still further embodiment of an apparatus for producing asilicon semiconductor single crystal according to the present invention,wherein a part (a) is a schematic cross-sectional explanatory view of anessential part thereof, and (b) is a perspective picked out view of anupper insulating member;

FIG. 5 is a graph showing a relationship between a temperature at acentral portion of a main growth surface to an upper growth furnace anda distance from a silicon melt surface in each of Example 1 andComparative Example 1; and

FIG. 6 is graphs each showing a relationship between an initial oxygenconcentration and an amount of precipitated oxygen in each of Example 1and Comparative Example 1, wherein a part (a) is a graph showing a rangeof from 0 to 25 cm of the constant diameter portion, a part (b) is agraph showing a range of from 25 to 75 cm of the constant diameterportion, and a part (c) is a graph showing a range of 75 cm or more ofthe constant diameter portion.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to growth examples of a silicon semiconductor single crystalby the CZ method illustrated in the accompanying drawings, but it is tobe noted that the present invention is not limited to these examples.For instance, an apparatus for producing a silicon semiconductor singlecrystal used for growing a silicon semiconductor single crystalaccording to the present invention can be naturally employed as anapparatus for producing a silicon semiconductor single crystal using themagnetic field applied Czochralski method (referred to as a MCZ methodhereinafter) in which a single crystal is grown by applying a magneticfield to silicon melt.

FIG. 1 is a schematic cross-sectional view showing an embodiment of anapparatus for producing a silicon semiconductor single crystal accordingto the present invention (may be referred to as a single crystalproducing apparatus). In FIG. 1, a single crystal producing apparatus 10comprises a main growth furnace 12 for growing a silicon semiconductorsingle crystal S, and an upper growth furnace 14 for housing and coolingdown a silicon semiconductor single crystal pulled therein. In thecenter of the main growth furnace 12 a crucible 18 which has a cruciblesupporting shaft 16 as a shaft and is composed of a quartz crucible 18 ainside and a graphite crucible 18 b outside is disposed rotatably andmovably up and down by a crucible driving mechanism 21 attached to alower edge of the crucible supporting shaft 16. Silicon melt M of astarting material for growing a silicon semiconductor single crystal Sis retained in the crucible 18. Further, a heater 20 made of graphite isarranged around the crucible 18. By making this heater develop heat,polysilicon charged in the crucible 18 is melted, and the siliconsemiconductor single crystal S is pulled from the obtained silicon meltM. A heater insulating member 22 is provided between the heater 20 andthe main growth furnace 12 to function for protecting the wall andkeeping warm the inside of the main growth furnace 12.

A wire reel mechanism 26 for winding or rewinding a wire 24 which pullsthe grown silicon semiconductor single crystal S is provided above theupper growth furnace 14. When growing a single crystal, the wire 24 isgradually wound up in the opposite direction of the crucible 18 whilebeing rotated to make the crystal grown under a seed crystal 26. A seedcrystal holder 28 for holding the seed crystal 26 is attached to a tipof the wire 24, and this seed crystal 26 is engaged with the wire 24 bymeans of this seed holder 28.

When a single crystal is grown, an inert gas such as Ar (Argon) isfilled in the growth furnace and a pressure inside the furnace isadjusted to a desired value to perform the growth operation; a gas flowrate control unit 30 and a conductance valve 32 for adjusting a flowrate of the inert gas and a pressure inside the furnace respectively areprovided outside the growth furnace, and thereby the flow rate and thepressure of the inert gas inside the growth furnace can be easilyadjusted to growth conditions.

When a silicon semiconductor single crystal S pulled from the siliconmelt M is cooled down, there is provided an upper insulating member 34for keeping warm a low temperature area of the crystal in the vicinityof a portion of the upper growth furnace 14 communicated to a ceilingsection 12 a of the main growth furnace 12 so that the upper insulatingmember 34 surrounds the silicon semiconductor single crystal S. Acharacteristic construction of the inventive apparatus resides in thisarrangement of the upper insulating member 34, and thereby a desiredcooling down temperature area is kept warm when the siliconsemiconductor single crystal S is passed therethrough.

As materials for the upper insulating member 34, insulating materialsshaped from carbon fiber are used for improving the keeping warm effect.The upper insulating member is covered with a coating of stainless steelfor preventing contamination inside the growth furnace to therebyinhibit flying of flocks from the carbon fiber or the like inside thegrowth furnace.

To make larger an amount of precipitated oxygen in the siliconsemiconductor single crystal S and make smaller distribution of anamount of precipitated oxygen in the direction of the growth axis, it ispreferable to provide the upper insulating member 34 at an area where atemperature in the upper growth furnace is 800° C. or less, morepreferably in the range from 400° C. to 650° C. It is also effective toprovide the upper insulating member 34 at an area where a temperature ofa grown crystal is 800° C. or less, more preferably in the range from400° C. to 650° C. in the upper growth furnace.

As materials used for covering the upper insulating member 34, inaddition to the above described stainless steel, high purity graphitematerials or high purity graphite materials with a surface coated withsilicon carbide or pyrolytic carbon may be used, and also metallicmaterials containing metals such as nickel, chromium, copper, titanium,tungsten, molybdenum or the like may be used.

To grow a silicon semiconductor single crystal S using the singlecrystal producing apparatus 10 as described above, at first polysiliconis charged in the crucible 18 disposed inside the main growth surface 12and an inert gas is filled in the furnace, and after that thepolysilicon is melted by making the heater 20 develop heat withadjusting a flow rate and a pressure of the inert gas flown into themain growth furnace 12. When the polysilicon is completely melted, thecrucible 18 retaining the silicon melt M is moved up and down to adjustit to a position suited for dipping the seed crystal 26 to the surfaceof the silicon melt M.

Then, a temperature of the silicon melt M is dropped to that suited fordipping the seed crystal 26 into the silicon melt M, and when thetemperature of the silicon melt is sufficiently stabilized, by rewindingthe wire 24 the seed crystal 26 is slowly dipped into the silicon melt Mand then stopped; after the temperature has been stabilized, while theseed crystal 26 and crucible 18 are slowly rotated in the oppositedirections, the wire 24 is gradually wound up, thus the siliconsemiconductor single crystal S being grown under the seed crystal 26.

When the silicon semiconductor single crystal S is grown, at first aneck portion 26 a is formed by gradually reducing the tip diameter ofthe seed crystal 26 to remove slip dislocations generated when the seedcrystal 26 is dipped into the silicon melt M. After the slipdislocations are removed from the grown crystal, a diameter of thecrystal grown under the seed crystal 26 is increased to a desired valueto form a seed-cone S1 of the silicon semiconductor single crystal S.After forming the seed-cone S1, there is grown a constant diameterportion S2 with almost cylindrical shape having a desired constantdiameter from which silicon semiconductor wafers are prepared. After theconstant diameter portion S2 having the desired length is grown, thecrystal diameter is reduced gradually to form an end-cone S3 in order toseparate the silicon semiconductor single crystal S from the siliconmelt M without adding thermal shock thereto.

After the formation of the end-cone S3 is completed and the siliconsemiconductor single crystal S is separated from the silicon melt M, thesilicon semiconductor single crystal S is slowly pulled into the uppergrowth furnace 14 to cool down it therein, and then the operation forgrowing the silicon semiconductor single crystal S is finished.

During growth of the silicon semiconductor single crystal S, to keep adiameter of the crystal constant and to stabilize quality of the crystalor thermal history imposed upon the silicon semiconductor single crystalS, the crucible driving mechanism 21 is operated so that a surface levelof the silicon melt M is kept constant.

FIG. 2 shows another example of the construction wherein the upperinsulating member 34 according to the inventive apparatus is attached tothe upper growth furnace 14. In the example shown in FIG. 2, the longupper insulating member 34 is detachably provided on a convex portion 36arranged in the upper growth section 14. FIG. 3 shows a further exampleof attachment of the upper insulating member 34 wherein the short upperinsulating member 34 is attached via the convex portion 36. With theabove described construction, the upper insulating member 34 may beeasily exchangeable in compliance with required quality of a siliconsemiconductor single crystal S to be grown.

FIG. 4 shows a still further example of arrangement of the upperinsulating member 34 in the inventive apparatus. In the example shown inFIG. 4, a plurality of upper insulating members 34 (three attached andone removed) are detachably attached to a plurality of convex portions36 (five in the example shown in the figure) arranged inside the uppergrowth furnace 14. In this case, by permitting installation and removalof the upper insulating member 34, it is possible to easily change anarea to be kept warm in the silicon semiconductor single crystal Shoused inside the upper growth furnace 14 or a length of the area to bekept warm in the direction of the crystal growth axis according as theoccasion may demand.

With the apparatus construction as shown in FIG. 2 to FIG. 4, atemperature area to be kept warm or a length thereof can be changedfreely. It is described in the examples shown in the figures that theform of the upper insulating member 34 is cylindrical. However, it isenough for the form of the upper insulating member 34 to surround thesilicon semiconductor single crystal S; there may be used such membersas ones formed by dividing a cylindrical body or an almost cylindricalbody with a horseshoe-shaped form as viewed from above. It should benoted that in FIG. 2 to FIG. 4, components identical with or similar tothose shown in FIG. 1 may be designated by the same reference numerals.

EXAMPLES

The present invention will be described in further details by way of thefollowing examples which should be construed illustrative rather thanrestrictive.

Experimental Example 1

To confirm the keeping warm effect of the upper insulating member 34provided in the upper growth furnace 14 according to the inventiveapparatus, with an apparatus similar to the one shown in FIG. 1,temperature distribution in the direction of the crystal growth axis atthe center in the furnace was measured in comparison with that of anormal single crystal producing apparatus not having the upperinsulating member 34. The length of the upper insulating member 34 was50 cm. The results are shown in FIG. 5.

As is apparent from the results of this measurement, it was confirmedthat, because of the effect of arranging the insulating member 34 insidethe upper growth furnace 14 of the single crystal producing apparatus10, the temperature distribution is gentle in the relatively lowtemperature region of the order of 300° C. to 600° C. Therefore, it isunderstood that, by growing a silicon semiconductor single crystal Susing the single crystal producing apparatus 10 according to the presentinvention, when the silicon semiconductor single crystal S is cooleddown, it receives low temperature thermal history longer than the casewhere the insulating member 34 is not provided in the upper growthfurnace 14.

Inventive Example 1

Next, using the inventive single crystal producing apparatus 10 providedwith the upper insulating member 34 shown in FIG. 1, a plurality (three)of silicon semiconductor single crystals S were grown.

A quartz crucible 18 with the inside diameter of 55 cm was disposed inthe main growth furnace 12 of the single crystal producing apparatus 10,120 kg of polysilicon was charged in the crucible 18, and thepolysilicon was melted by making the heater 20 develop heat to becomesilicon melt M. Then, after a temperature of the silicon melt M wasstabilized, the seed crystal 26 was dipped into a surface of the siliconmelt M and then was pulled therefrom to make a silicon semiconductorsingle crystal S with the constant diameter portion S2 of 100 cm inlength and 200 mm in diameter grow under the seed crystal 26. Thecrystal growth was performed such that the pulling rate of the constantdiameter portion S2 of the silicon semiconductor single crystal S standsat 0.9 to 1.0 mm/min; after growth of the silicon semiconductor singlecrystal S was over, the constant diameter portion S2 of the siliconsemiconductor single crystal S was processed into wafers, and an amountof precipitated oxygen at the center of the crystal was measured. Themeasuring results of three grown silicon semiconductor single crystalsare shown in FIG. 6.

In FIG. 6, assuming that the seed crystal side leading edge of theconstant diameter portion S2 of the silicon semiconductor single crystalS stands at 0 cm, the area ranging from 0 to 25 cm of the constantdiameter portion S2 is defined as the first half section, the arearanging from 25 cm to 75 cm of the constant diameter portion S2 as themiddle section, and the area ranging from 75 cm to the terminal edge ofthe constant diameter portion S2 as the second half section; amounts ofprecipitated oxygen against the initial oxygen concentrations of therespective silicon semiconductor single crystals S are shown in FIGS.6(a), (b) and (c), respectively.

The conditions for heat treatment applied to the sample wafers formeasuring an amount of precipitated oxygen were 600° C. for 180minutes+1000° C. for 60 minutes+1100° C. for 180 minutes, and themeasurement was performed after the heat treatment. An amount ofprecipitated oxygen was calculated in a manner that the oxygenconcentrations before and after the heat treatment were measured bymeans of infrared absorption spectroscopy, subtracting the value afterthe heat treatment from that before the heat treatment.

Comparative Example 1

Silicon semiconductor single crystals (three) each with 200 mm indiameter and 100 cm in length of the constant diameter portion weregrown under the same conditions as those in Example 1 excluding that theupper insulating member 34 was removed from the upper growth furnace 14of the single crystal producing apparatus 10 shown in FIG. 1. Aftergrowth of the silicon semiconductor single crystal S was over, samplewafers for confirming amounts of precipitated oxygen were sliced fromthe respective areas of the crystal as in Inventive Example 1; then thewafers were subjected to heat treatment and measured in terms of amountsof precipitated oxygen. The measuring results of three grown siliconsemiconductor single crystals are shown in FIG. 6.

In the graphs of FIG. 6, assuming that the seed crystal side leadingedge of the constant diameter portion S2 of the silicon semiconductorsingle crystal S stands at 0 cm, the area ranging from 0 to 25 cm of theconstant diameter portion S2 is defined as the first half section, thearea ranging from 25 cm to 75 cm of the constant diameter portion S2 asthe middle section, and the area ranging from 75 cm to the terminal edgeof the constant diameter portion S2 as the second half section; amountsof precipitated oxygen against the initial oxygen concentrations of therespective silicon semiconductor single crystals S are shown in FIGS.6(a), (b) and (c), respectively; the conditions for heat treatmentapplied to the sample wafers for measuring an amount of precipitatedoxygen were 600° C. for 180 minutes+1000° C. for 60 minutes+1100° C. for180 minutes as in Inventive Example 1.

From the above described results, it is understood that, as comparedwith the silicon semiconductor single crystal S grown using the singlecrystal producing apparatus without providing the upper insulatingmember 34 in the upper growth furnace 14 shown in Comparative Example 1,the amounts of precipitated oxygen over the entire constant diametersection S2 of the silicon semiconductor single crystal grown in Example1 were more, and that amounts of precipitated oxygen in both the firsthalf section and the second half section are highly homogeneous.Further, it was confirmed that, when the upper insulating member 34 wasprovided in the upper growth furnace 14, single crystal growth isperformed without creation of such problems as slip dislocations occurin the course of growth of the silicon semiconductor single crystal S,and provision of the upper insulating member 34 does not create suchtroubles as crystal growth is hindered due to loss of heat balance inthe single crystal producing apparatus.

Over against this, from the results of Comparative Example 1 it isunderstood that, as compared with Example 1, the amounts of precipitatedoxygen are smaller, the amount of precipitated oxygen in the first halfsection of the constant diameter section is lower than that in thesecond half section thereof, and a variation of the amounts ofprecipitated oxygen in the direction of the crystal growth axis ispresent. Further, in Comparative Example 1 the amounts of precipitatedoxygen themselves stand generally at low values.

It should be noted that the present invention is not limited to theembodiments described above. The embodiments described above are givenonly for illustrative purposes, and it is needless to say that any typeof single crystal producing apparatus having the substantially sameconstruction and the same effect as technical ideas stated in theattached claims should be considered to be within the technical scope ofthe present invention.

For example, there were described the seed crystal used for growing asilicon semiconductor single crystal and the method for producing thesilicon semiconductor single crystal according to the present inventionby means of an example of the CZ method in which a silicon semiconductorsingle crystal is pulled from the silicon melt without applying amagnetic field to the silicon melt, but it is needless to say that thesame effect can be obtained in production of silicon semiconductorsingle crystals by the MCZ method in which a single crystal is grownwhile applying a magnetic field to the silicon melt.

Capability of Exploitation In Industry:

As described above, when the apparatus for producing a siliconsemiconductor single crystal according to the present invention is usedfor growing a silicon semiconductor single crystal by the CZ method, itis possible to grow a homogeneous silicon semiconductor single crystalwith stable distribution of an amount of precipitated oxygen along thefull length of the crystal without adding an expensive and complicatedapparatus to a silicon semiconductor single crystal producing apparatus,nor introducing an apparatus, for instance, for conducting heattreatment on the grown silicon semiconductor single crystal; it is alsopossible to manufacture an excellent silicon semiconductor wafer havinga small quality variation at low cost and without the need for changingthe manufacturing process.

Further, the inventive apparatus has the ability to easily supplysilicon semiconductor single crystals with an increased amount ofprecipitated oxygen as compared with the conventional one; when wafersobtained from the silicon semiconductor single crystals are used forfabricating semiconductor devices, it is possible to increase the deviceyield and also to improve quality of the semiconductor devices.

What is claimed is:
 1. A method for producing a silicon semiconductorsingle crystal by the Czochralski method, comprising the steps of:growing the silicon semiconductor single crystal pulled from a crucible;and keeping warm a portion thereof with a temperature of 800° C. or lesswithout heating it from the outside.
 2. A method for producing a siliconsemiconductor single crystal, comprising the step of: producing thesilicon semiconductor single crystal by the use of apparatus forproducing a silicon semiconductor single crystal including: a maingrowth furnace having a crucible retaining silicon melt disposed thereinfor growing a silicon semiconductor single crystal; and an upper growthfurnace for housing therein and cooling the silicon semiconductor singlecrystal pulled from the silicon melt, wherein the upper growth furnacedisposed above and communicated to a ceiling section of the main growthfurnace is provided with an upper insulating member for surrounding apulled silicon semiconductor single crystal.
 3. A method for producing asilicon semiconductor single crystal according to claim 2, wherein alength in a direction along the crystal growth axis of the upperinsulating member provided in the upper growth furnace ranges betweenone-twentieth of the full length of the upper growth furnace and thefull length of the upper growth furnace.
 4. A method for producing asilicon semiconductor single crystal according to claim 2, wherein theupper insulating member provided in the upper growth furnace is providedat a position where a temperature inside the upper growth furnace is800° C. or less.
 5. A method for producing a silicon semiconductorsingle crystal according to claim 2 wherein the upper insulating memberprovided in the upper growth furnace is provided at a position where atemperature inside the upper growth furnace is in the range from 400° C.to 650° C.
 6. An apparatus for producing a silicon semiconductor singlecrystal by the Czochralski method comprising: a main growth furnacehaving a crucible retaining silicon melt disposed therein for growing asilicon semiconductor single crystal; and an upper growth furnace forhousing therein and cooling the silicon semiconductor single crystalpulled from the silicon melt, wherein the upper growth furnace disposedabove and communicated to a ceiling section of the main growth furnaceis provided with an upper insulating member for surrounding a pulledsilicon semiconductor single crystal.
 7. The apparatus for producing asilicon semiconductor single crystal according to claim 6, wherein alength in a direction along the crystal growth axis of the upperinsulating member provided in the upper growth furnace ranges betweenone-twentieth of the full length of the upper growth furnace and thefull length of the upper growth furnace.
 8. The apparatus for producinga silicon semiconductor single crystal according to claim 7, wherein asurface of the upper insulating member provided in the upper growthfurnace is covered with high purity graphite materials or high puritygraphite materials with a surface coated with a film of pyrolytic carbonor silicon carbide.
 9. The apparatus for producing a siliconsemiconductor single crystal according to claim 6, wherein a surface ofthe upper insulating member provided in the upper growth furnace iscovered with high purity graphite materials or high purity graphitematerials with a surface coated with a film of pyrolytic carbon orsilicon carbide.
 10. An apparatus for producing a silicon semiconductorsingle crystal by the Czochralski method comprising: a main growthfurnace having a crucible retaining silicon melt disposed therein forgrowing a silicon semiconductor single crystal; and an upper growthfurnace for housing therein and cooling the silicon semiconductor singlecrystal pulled from the silicon melt, wherein the upper growth furnacecommunicated to a ceiling section of the main growth furnace is providedwith an upper insulating member for surrounding a pulled siliconsemiconductor single crystal and wherein the upper insulating memberprovided in the upper growth furnace is provided at a position where atemperature inside the upper growth furnace is 800° C. or less.
 11. Theapparatus for producing a silicon semiconductor single crystal accordingto claim 10, wherein the upper insulating member provided in the uppergrowth furnace is provided at a position where a temperature inside theupper growth furnace is in the range from 400° C. to 650° C.
 12. Theapparatus for producing a silicon semiconductor single crystal accordingto claim 11, wherein the upper insulating member provided in the uppergrowth furnace is made of materials obtained by shaping carbon fiber.13. The apparatus for producing a silicon semiconductor single crystalaccording to claim 11, wherein a surface of the upper insulating memberprovided in the upper growth furnace is covered with high puritygraphite materials or high purity graphite materials with a surfacecoated with a film of pyrolytic carbon or silicon carbide.
 14. Theapparatus for producing a silicon semiconductor single crystal accordingto claim 11, wherein a surface of the upper insulating member providedin the upper growth furnace is covered with metallic materialscontaining a metal selected from the group consisting of iron, nickel,chromium, copper, titanium, tungsten, and molybdenum as the mainingredient.
 15. The apparatus for producing a silicon semiconductorsingle crystal according to claim 11, wherein the upper insulatingmember provided in the upper growth furnace is exchangeable incompliance with a selected cooling thermal history of a siliconsemiconductor single crystal.
 16. The apparatus for producing a siliconsemiconductor single crystal according to claim 11, wherein a pluralityof the upper insulating members are provided along the siliconsemiconductor single crystal growth axis in the upper growth furnace andthe number of the upper insulating members provided along the siliconsemiconductor single crystal growth axis is adjustable in compliancewith a selected cooling thermal history of the silicon semiconductorsingle crystal.
 17. The apparatus for producing a silicon semiconductorsingle crystal according to claim 10, wherein the upper insulatingmember provided in the upper growth furnace is made of materialsobtained by shaping carbon fiber.
 18. The apparatus for producing asilicon semiconductor single crystal according to claim 10, wherein asurface of the upper insulating member provided in the upper growthfurnace is covered with high purity graphite materials or high puritygraphite materials with a surface coated with a film of pyrolytic carbonor silicon carbide.
 19. The apparatus for producing a siliconsemiconductor single crystal according to claim 10, wherein a surface ofthe upper insulating member provided in the upper growth furnace iscovered with metallic materials containing a metal selected from thegroup consisting of iron, nickel, chromium, copper, titanium, tungsten,and molybdenum as the main ingredient.
 20. The apparatus for producing asilicon semiconductor single crystal according to claim 10, wherein theupper insulating member provided in the upper growth furnace isexchangeable in compliance with a selected cooling thermal history of asilicon semiconductor single crystal.
 21. The apparatus for producing asilicon semiconductor single crystal according to claim 10, wherein aplurality of the upper insulating members are provided along the siliconsemiconductor single crystal growth axis in the upper growth furnace andthe number of the upper insulating members provided along the siliconsemiconductor single crystal growth axis is adjustable in compliancewith a selected cooling thermal history of the silicon semiconductorsingle crystal.
 22. An apparatus for producing a silicon semiconductorsingle crystal by the Czochralski method comprising: a main growthfurnace having a crucible retaining silicon melt disposed therein forgrowing a silicon semiconductor single crystal; and an upper growthfurnace for housing therein and cooling the silicon semiconductor singlecrystal pulled from the silicon melt, wherein the upper growth furnacecommunicated to a ceiling section of the main growth furnace is providedwith an upper insulating member for surrounding a pulled siliconsemiconductor single crystal and wherein the upper insulating memberprovided in the upper growth furnace is made of materials obtained byshaping carbon fiber.
 23. An apparatus for producing a siliconsemiconductor single crystal by the Czochralski method comprising: amain growth furnace having a crucible retaining silicon melt disposedtherein for growing a silicon semiconductor single crystal; and an uppergrowth furnace for housing therein and cooling the silicon semiconductorsingle crystal pulled from the silicon melt, wherein the upper growthfurnace communicated to a ceiling section of the main growth furnace isprovided with an upper insulating member for surrounding a pulledsilicon semiconductor single crystal, wherein a length in a directionalong the crystal growth axis of the upper insulating member provided inthe upper growth furnace ranges between one-twentieth of the full lengthof the upper growth furnace and the full length of the upper growthfurnace and wherein the upper insulating member provided in the uppergrowth furnace is made of materials obtained by shaping carbon fiber.24. An apparatus for producing a silicon semiconductor single crystal bythe Czochralski method comprising: a main growth furnace having acrucible retaining silicon melt disposed wherein for growing a siliconsemiconductor single crystal; and an upper growth furnace for housingtherein and cooling the silicon semiconductor single crystal pulled fromthe silicon melt, wherein the upper growth furnace communicated to aceiling section of the main growth furnace is provided with an upperinsulating member for surrounding a pulled silicon semiconductor singlecrystal and wherein a surface of the upper insulating member provided inthe upper growth furnace is covered with metallic materials containing ametal selected from the group consisting of iron, nickel, chromium,copper, titanium, tungsten, and molybdenum as the main ingredient. 25.An apparatus for producing a silicon semiconductor single crystal by theCzochralski method comprising: a main growth furnace having a crucibleretaining silicon melt disposed therein for growing a siliconsemiconductor single crystal; and an upper growth furnace for housingtherein and cooling the silicon semiconductor single crystal pulled fromthe silicon melt, wherein the upper growth furnace communicated to aceiling section of the main growth furnace is provided with an upperinsulating member for surrounding a pulled silicon semiconductor singlecrystal, wherein a length in a direction along the crystal growth axisof the upper insulating member provided in the upper growth furnaceranges between one-twentieth of the full length of the upper growthfurnace and the full length of the upper growth furnace and wherein asurface of the upper insulating member provided in the upper growthfurnace is covered with metallic materials containing a metal selectedfrom the group consisting of iron, nickel, chromium, copper, titanium,tungsten, and molybdenum as the main ingredient.
 26. An apparatus forproducing a silicon semiconductor single crystal by the Czochralskimethod comprising: a main growth furnace having a crucible retainingsilicon melt disposed therein for growing a silicon semiconductor singlecrystal; and an upper growth furnace for housing therein and cooling thesilicon semiconductor single crystal pulled from the silicon melt,wherein the upper growth furnace communicated to a ceiling section ofthe main growth furnace is provided with an upper insulating member forsurrounding a pulled silicon semiconductor single crystal and whereinthe upper insulating member provided in the upper growth furnace isexchangeable in compliance with a selected cooling thermal history of asilicon semiconductor single crystal.
 27. An apparatus for producing asilicon semiconductor single crystal by the Czochralski methodcomprising: a main growth furnace having a crucible retaining siliconmelt disposed therein for growing a silicon semiconductor singlecrystal; and an upper growth furnace for housing therein and cooling thesilicon semiconductor single crystal pulled from the silicon melt,wherein the upper growth furnace communicated to a ceiling section ofthe main growth furnace is provided with an upper insulating member forsurrounding a pulled silicon semiconductor single crystal, wherein alength in a direction along the crystal growth axis of the upperinsulating member provided in the upper growth furnace ranges betweenone-twentieth of the full length of the upper growth furnace and thefull length of the upper growth furnace and wherein the upper insulatingmember provided in the upper growth furnace is exchangeable incompliance with a selected cooling thermal history of a siliconsemiconductor single crystal.
 28. An apparatus for producing a siliconsemiconductor single crystal by the Czochralski method comprising: amain growth furnace having a crucible retaining silicon melt disposedtherein for growing a silicon semiconductor single crystal; and an uppergrowth furnace for housing therein and cooling the silicon semiconductorsingle crystal pulled from the silicon melt, wherein the upper growthfurnace communicated to a ceiling section of the main growth furnace isprovided with an upper insulating member for surrounding a pulledsilicon semiconductor single crystal and wherein a plurality of theupper insulating members are provided along the silicon semiconductorsingle crystal growth axis in the upper growth furnace and the number ofthe upper insulating members provided along the silicon semiconductorsingle crystal growth axis is adjustable in compliance a selectedcooling thermal history of the silicon semiconductor single crystal. 29.An apparatus for producing a silicon semiconductor single crystal by theCzochralski method comprising: a main growth furnace having a crucibleretaining silicon melt disposed therein for growing a siliconsemiconductor single crystal; and an upper growth furnace for housingtherein and cooling the silicon semiconductor single crystal pulled fromthe silicon melt, wherein the upper growth furnace communicated to aceiling section of the main growth furnace is provided with an upperinsulating member for surrounding a pulled silicon semiconductor singlecrystal, wherein a length in a direction along the crystal growth axisof the upper insulating member provided in the upper growth furnaceranges between one-twentieth of the full length of the upper growthfurnace and the full length of the upper growth furnace and wherein aplurality of the upper insulating members are provided along the siliconsemiconductor single crystal growth axis in the upper growth furnace andthe number of the upper insulating members provided along the siliconsemiconductor single crystal growth axis is adjustable in compliancewith a selected cooling thermal history of the silicon semiconductorsingle crystal.